How do I stop caring?

So, I’m in a frat and my biggest issue is I’ll do anything for my friends, whether driving people home at 3 AM, or doing things around the frat to keep it nice and clean. I genuinely enjoy being there for people—but here’s the issue: I think I’ve let people walk all over me, and I’m just now realizing it.

When it comes to girls, I’m the guy who’s always there to listen. If they’re having a bad day, I’m the first one to lend a shoulder. And when I like someone, I’ll go all out to be helpful. Like, a few weeks ago, the girl I have a crush on (and had made it seem to everyone else that she liked me back) asked me if I would be willing to let her friends use my apartment for her friends birthday party. Hers was too small and didn’t have as much seating as my place. At the end of the night she didn’t even thank me just kind of brushed it off, like it was no big deal. And left me to clean all the dishes. But I didn’t even feel upset. I just felt good to have helped.

Then with another girl I was so wrapped around her finger because she did all the right things and said all the right things to make me think she liked me back but was just using me for attention and stuff like that.

I do get frustrated, but I don’t know how to voice it. I have trouble saying "no" to people without feeling like I’m being rude or selfish. So, I keep overextending myself and end up drained. I’ve always been the "nice guy," but lately, I’m starting to see how much it’s affecting me. I just don’t want to come across as mean, so I keep putting others’ needs before my own—and I think it’s starting to get to me.

I’ve been thinking a lot about how I can stand up for myself more without feeling like I’m being a jerk. I know being nice is a good thing, but I’m realizing it’s not about being a doormat. I need to learn how to set boundaries and not be afraid to say "no" when I need to.

Has anyone else been in the same boat? How did you find the balance between being a good person and not letting people take advantage of your kindness? I really want to figure this out, but I’m not sure where to start.